Influenza, avian influenza, varicella, and SARS belong not only to the most virulent viruses known to human kind but are also spread by the airborne route. Strategies to prevent and control the oftenexplosive outbreaks associatedwith these pathogens are limited to vaccination and treatment, if available, or isolation and barrier precautions. The latter includes the utilization efface masks to interrupt the chain of transmission. However, the scientific evidence regarding the efficacy of face masks has been solely based on studies using mannequin heads and non-viable tracers and/or bacteria. ; We propose to develop a model for the airborne dispersal of viable viral pathogens (human rhinovirus) and for testing the efficacy of barrier precautions such as face masks in human subjects. In the first aim, we will establish a test procedure to disperse particles in defined sizes (1 and 10 urn) containing preset amounts of rhinovirus. The particle sizes represent transmission by droplet (10 urn) or small particles (1 urn). Dispersal will be measured by a particle counter, and two air sampling methods, impaction and impingement. In the second aim, the dose-response curve of the human infectious dosage (HID) will be determined by exposure of human subjects to defined rhinovirus concentrations in the particle size of 1pm. Participants will be selected 1oreflect a representative group regarding susceptibility to rhinovirus. In the third aim, we propose to study the efficacy of face masks and fit-testing_procedures'*by exposure to 1 urn particles containing tiinovirus. First, the relevance of the transocular route will be determined by wearing eye protection during exposure to the rhinovirus (HID80). Participants will then be enrolled in intervention groups undergoing exposure to rhinovirus while wearing surgical masks or N 95 respirators with and without fit-testing. This proje<rt is the first attempt to develop a method for evaluation of the utility and efficacy effacemasks and fit-testing using a viable pathogen in human subjects. Furthermore, an improved understanding of the pathology of airborne viruses allows for a better risk assessment of transmission via the airborne route. This cnowledge is paramount in view of the inevitable viral pandemics.